Multi-stage pump



Dec. 6, 1966 WY v. MILLMAN 3,289,923

MULTI-STAGE PUMP Filed Oct. 30, 1964 2 Sheets-Sheep 1 INVENTOR. 3O WILLIAM V. MiLLMAN ATTORNEY FIG.3

Dec. 6, 1966 w. v. MILLMAN 3,289,923

MULTISTAGE PUMP Filed Oct. 30, 1964 2 Sheets-Sheet 2 INVENTOR.

WILLIAM V. MILLMAN ATToRNY United States Patent 3,289,923 MULTl-STAGE PUMP William V. Millman, Molina, Ill., assignor to American Air Filter Company, Inc., Louisville, Ky, a corporation of Delaware Filed Oct. 30, 1964, Ser. No. 407,764 6 Claims. (Cl. 23013l) This invention relates to a multi-stage pump or compressor.

Many conventional multi-stage compressors are provided with a diffuser arrangement in which'the difiuser channels, with or without vanes, are disposed radially about and in line with the impellers of the pumping stage. The flow in such multi-stage compressors is generally radially outwardly from the impeller, then at a right angle .in a direction axially of the housing, and then inwardly to the inlet of the succeeding pumping stage. The housings for such arrangements are generally concentric about the axis of rotation of the impellers and are of heavy cast construction. Typically, the cast housing includes surfaces which must be machined to close tolerances to provide precision fits.

An object of the present invention is to provide a multistage compressor construction which lends itself to fabrication out of relatively inexpensive sheet form material, and which is operable with reasonable efficiency without the requirements of close tolerances or fits in the assembly.

Another object is the provision of a low flow-high head centrifugal compressor of multi-stage design of a character which accommodates selecting as many or as few stages as necessary to accomplish the intended result.

Another object is the provision of an arrangement in which the well-recognized scroll or volute configuration, known to yield eflicient results in simple centrifugal fans, is incorporated in a multi-stage design to good advantage.

In accordance with my invention, I provide an arrangement in which each stage of the multi-stage arrangement includes a pumping section formed of an impeller surrounded by a volute, and a successive diffusing section which includes both a diffuser segment and a lead-in segment, with the outlet of the volute of the pumping stage being connected through a gradual and smooth flow transfer zone to the inlet of the diffusion section. A feature of the arrangement is the provision of flow passages in which cross-sectional changes are made gradually, and in which the passages are generally aligned so that as the flow progresses circumferentially and in succession through the volute, transfer duct, diffuser segment and lead-in segment, abrupt changes in flow direction are substantially minimized.

A multi-stage compressor according to the invention may include, for example, a right cylindrical outer casing containing a series of substantially flat, axially spaced walls arranged transverse to the axis of the casing to divide the easing into alternate pumping layers and intermediate diffusing layers. Each pumping layer includes an impeller surrounded by a volute formed by an outwardly spiralling vane and terminating in a peripheral outlet connected through a transfer duct to the peripheral inlet of the succeeding intermediate ditfusing layer. The transfer duct progresses relatively gradually in an axial direction as it progresses substantially farther in a circumferential direction so that it resembles a ramp. Each difiusing layer includes a series of inwardly spiralling vanes defining, in the direction of flow, first a diffusing fer duct wall.

3,289,923 Patented Dec. 6, 1966 segment providing an increasing cross-sectional area due to a correspondingly increasing radial dimension, and then a lead-in segment of substantially constant crosssection leading to the eye of the succssive pumping layer. The apparatus may be viewed as a series of sandwiches stacked in the casing, with each sandwich comprising a pumping layer and a diffusing layer. Each such sandwich is aligned with the next sandwich, with the axes of the successive impellers aligned but offset with respect to the central axis of the cylindrical casing, since the axis of the casing does not correspond to the axis of rotation of the impellers.

Another feature of the construction is that the outwardly spiralling vanes of the pumping layers and the inwardly spiralling vanes of the dilfusing layers not only define boundaries of flow passages but also serve as structural members which lend strength to the assembly to withstand the pressures developed. A further benefit of the invention is that the volute housing arrangement permits a wide range of operating conditions, much like the vaneless diffuser, before encountering a surging point.

An example of apparatus incorporating an embodi= ment of the invention by way of example is illustrated in the accompanying drawing in which:

FIGURE 1 is a partly broken perspective view of a single sandwich incorporating a pumping layer and a diffusing layer and with the impeller for the sandwich exploded;

FIGURE 2 is a view of a casing having a series of assembled sandwiches shown in outline form therewithin, and with parts of several sandwiches schematically shown to illustrate the flow path of the fluid;

FIGURE 3 is a section of the hub portion of a series of sandwiches in assembled relation;

FIGURE 4 is a plan view of the pumping layer; and

FIGURE 5 is a plan view of the diffusing layer.

In the drawing, FIGURE 1 shows an assembled sandwich 10 with the impeller 11 exploded therefrom. Each sandwich 10 forms one stage of the multi-stage pump as indicated in FIGURE 2, and each is substantially the same in form although successive sandwiches in the direction of flow will normally have progressively less depth, i.e., thickness, depending upon the particular fluid to be handled and the extent to which it is compressible.

Each sandwich essentially includes an upstream pumping layer 12 and an underlying and downstream diffusing layer 14 (FIGS. 1 and 2) with the communication between the pumping layer and diffusing layer being through means of the ramp-shaped transfer zone generally designated 16 adjacent the periphery of the sandwich. The communication from the diffusing layer of one sandwich to the pumping layer of the next successive sandwich is through the central opening in the back wall of the diffusing layer.

The boundaries between the layers are defined by the disc-shaped plates or walls 18 and 20. The back wall 18 of the pumping layer is substantially flat and is imperforate except for a slightly off center opening 22 which accommodates the hub of the impeller in the manner to be later explained, and a somewhat arcuateshaped opening 24 extending for a short distance along the outer margin of the layer and underlying the trans- An outwardly spiralling vane 26 is disposed with its leading end adjacent the inner edge of the opening 24 for the transfer zone, and gradually progresses circumferentially and radially outwardly to a termination point at the periphery of the layer about three fourths of the way around the circle of the layer. Vane 26 forms the volute providing a generally expanding cross-sectional area between the periphery of the impeller (indicated in FIG. 4 by the broken lines) and the vane. Flow into each pumping layer is through the eye of the impeller. The outlet of each pumping layer coincides with the entrance 28 to the transfer zone 16.

The diffusing layers, which alternate with the pumping layers, are here so termed because their principal function from a performance standpoint is to provide space for continued diffusion of the fluid before entrance into the next pumping layer. However, the lead-in function performed by these layers in gradually directing the fluid into the successive pumping layers while avoiding abrupt changes in cross section or obstacles to flow is perhaps equally important.

The wall (FIGS. 1, 3, 5) between a diffusing layer and the succeeding pumping layer is more or less disc shaped, and is flat except for the flanged edge on the central outlet opening 30, and the sloping lower ramp wall 32 of the transfer zone. The inlet to the diffusing layer coincides with the outlet of the transfer duct and is generally indicated by the numeral 34 in FIGURE 5.

In one currently preferred arrangement, a series of three vanes 36, 38 and 40 are arranged to spiral inwardly to the outlet from circumferentially spaced locations around the periphery of the diffusing layer. The number of vanes used will normally be determined by the diameter of the pump. These vanes stand on edge and are sandwiched between the two walls 18 and 20 when the layers are assembled. The vanes form diffusing passages with the periphery of the layer, and lead-in passages to the outlet for the rest of their length. The first diffusing passage of expanding cross-sectional area is defined between the vane 36 and the periphery of the layer and begins at the outlet of the transfer duct. This first diffusing passage ends where the leading end of the vane 38 is reached. As shown, vane 38 is disposed with its leading end spaced radially outwardly from the vane 36 slightly more than half ofithe distance toward the periphery of the layer, and the vanes 36 and 38 run substantially parallel to each other for the remainder of the distance to the outlet of the diffusing layer. The spaces between the vanes are termed lead-in passages and they are of substantially constant cross-sectional area. However, a second diffusion passage of expanding cross sectional area is formed between the outside surface of the second vane 38 and the periphery of the layer until the leading edge of vane 40 (at the periphery of the layer) is reached. At this point the second lead-in passage of substantially constant cross-sectional area is formed between the vanes 38 and 40 as they progress to the outlet of the diffusing layer. Then, for an additional circumferential distance a third diffusing passage is formed between the third vane 40 and the periphery of the diffusing layer until the point where the leading edge of vane 36 is reached. There the third lead-in passage of substantially constant cross-sectional area is formed between the vanes 36 and 40. It will thus be apparent that for well over 180 degrees of the circumferential progression of the fluid around the diffusing layer, part of the fluid is moving in expanding crosssectional area passages. The remaining fluid is channelled by the lead-in passages to the outlet of the diffusing layer.

Each sandwich is circumscribed by a ring 42 having the same depth as a single sandwich. The width of each ring is indicated in FIGURE 3. While the ring is shown around both FIGURES 4 and 5 for comparison, a single ring is used in the assembly of the two layers.

vfor a scroll development.

All of the stationary parts of a sandwich are rigidly fixed to each other. While the particular bonding scheme used depends upon the materials of which the sandwich is fabricated, an epoxy type bonding material has been found generally satisfactory for a small device.

The impeller 11 (FIGS. 1 and 3) for each pumping stage is mounted on the common shaft 44 and includes a hub 46 of generally spool-like shape, a flat, circular back plate 48 affixed securely to the hub, and a series of generally radially extending blades 50 which abut the hub at their inner ends, but terminate short of the periphery of the back plate at their outer ends to provide an annular space 52 at the periphery of the impeller between the back plate 48 and the front plate 54. The front plate has the same outer diameter as the back plate but has a flanged central opening 56 which serves to provide, with the oppositely directed and slightly smaller flanged outlet 30 of the diffusing layer back wall 20, an overlapping seal as is best shown in FIGURE 3. A somewhat better seal more like a labyrinth may be pro vided by the addition of a ring (not shown) diametrically larger than flanged rim 56 of the impeller front plate, and attached to the back of the wall 20 in concentric relation to the rim.

Shown in FIGURE 3, hub 46 is provided with a boss 58 on one end face and a correspondingly dimensioned recess 60 on its opposite end so that in assembled form upon the shaft 44 the hubs interfit with each other. Each hub boss may be provided with a set screw for securing the hub to the shaft.

In the generally outline view of FIGURE 2 a series of sandwiches 10 are shown in assembled relation within the outer cylindrical casing 62 and upon the shaft 44 of motor 64. The order of assembly is first the upstream impeller is locked on the shaft, then the first sandwich, then another impeller, then the next sandwich, and so on. Each sandwich is aligned with the others with all transfer zones being aligned also. An adhesive sealing material is provided between the rim edges of the outer rings 42 and the downstream face peripheral margins of the walls 20 as each of the sandwiches is inserted. Each hub 46 is also locked to the motor shaft 44. In FIGURE 2 the sandwich closest to the motor 64 is the first stage sandwich and is fed centrally through the space between the motor and the upstream wall of the casing. The fluid discharge is out of the central opening 30 of the last stage sandwich as indicated. In addition to using an adhesive to secure stages together internally, clamps 66 are provided to bear against the downstream wall 20 of the last diffuser layer.

The general flow path of the fluid handled is indicated 'by the arrows in both the broken away parts of FIGURE 2 and in the sectioned portion of FIGURE 3. The hub 46a at the inlet to the casing, and 46b at the outlet are rounded to promote smooth entering and leaving flow. If desired, the last diffusing layer may be replaced by a take-01f which receives the discharge from the last pump tangentially rather than through the central outlet.

As shown in FIGURE 3, it will normally be found preferable when handling compressible fluids to provide sandwich depths which progressively decrease in the direction of fluid flow to accommodate the decreasing volumetric capacity required in successive stages. In the device shown the decrease is mainly provided by decreasing thickness impellers and pumping layers.

An important factor in the construction of the device is that the impeller and motor shaft axis does not correspond with the axis of the casing 62. In constructing the device, the scroll development for each pumping stage is calculated according to one of the conventional formulas Then the diameter of a circumscribing circle is determined by adding the longest radius of the scroll to the aligned radius. A circle with that diameter corresponds to the inner diameter of the outer ring 42. The center of the circumscribing ring 42 is offset relative to the center of the impeller tothe degree indicated in FIGURES 4 and 5 where the ring center is indicated by numeral 68. On one satisfactorily operating device having a diameter of about 24 inches, the centers are offset from each other about 1 inch. Thus it will be appreciated that the central inlets and outlets of the stages is intended to designate only their approximate positions. The scroll outline and circle do not 00- incide exactly, but the differences are of an order which may be neglected in the character of construction with which the invention is concerned.

In operation, fluid handled by the device flows in a continuing circular motion as it moves axially in a substantially shorter distance from inlet to outlet. The rotary motion is imparted to the fluid first by the upstream impeller. The fluid passes around the volute and then through the transfer duct to the diffusion layer. It is important to note that the transfer duct provides a passage which progresses to a substantial degree in a circumferential direction as compared to the slight progression in the axial direction. As a result the fluid is led gradually and smoothly from the pumping layer to the diffusion layer. There the smooth circular flow continues as guided by the vanes to the inlet of the next impeller.

A pump according to the described construction combines the features of inexpensive construction, substantial strength, compactness, and reasonable efficiency. The sheet metal approach results in substantially reduced cost as compared to cast, machined and polished parts. The sandwich, and layers with vanes, construction provides adequate strength to the assembly, and results in compactness with little waste space. Except for the final downstream wall of the assembly, the pressure difference on opposite sides of the transverse walls are only those differences between stages, and the cylindrical casing construction provides maximum strength in the radial direction. The efficiency results from taking advantage of the scroll configuration and providing an arrangement in which the angular momentum of the fluid is preserved, both in the layers, and in the transfer zone between layers.

I claim: 1. A multi-stage pumping device comprising: a right cylindrical outer casing; at least one fluid conducting stage in said casing, each stage including means defining an upstream pumping chamber and a downstream diffusing chamber;

each pumping chamber including a fluid impeller c0- operatively mounted for rotation in said pumping chamber, a central fluid inlet disposed to conduct fluid to said impeller and a vane spiralling radially outward about a portion of the periphery of said impeller and forming a volute between said vane and said outer casing, said vane terminating in a generally tangentially directed pumping chamber outlet adjacent the periphery of said impeller;

means defining an unobstructed transfer duct communicating with said pumping chamber outlet and forming a substantial continuation of said volute around the periphery of said stage but progressing gradually in an axial direction to a generally tangentially directed fluid outlet from said transfer duct in said diffusing chamber; and

each diffusing chamber having a series of inwardly spiralling vanes disposed to provide first passage of expanding cross section area between one of said vanes and the outer casing of said chamber and then forming passages of uniform cross-sectional area between adjacent vanes, said vanes terminating in an outlet from said diffusing chamber which forms a cooperative intake for the next stage.

2. A multi-stage pumping device comprising:

a right cylindrical outer casing;

at least one fluid conducting stage in said casing, each such stage including means defining an upstream pumping chamber and a downstream diffusing chamber;

each pumping chamber including a fluid impeller cooperatively mounted for rotation in said pumping chamber, a central fluid inlet disposed to conduct fluid to said impeller and a vane spiralling radially outwardly about a portion of the periphery of said impeller and forming a volute between said vane and said outer casing, said vane terminating in a generally tangentially directed pumping chamber outlet adjacent the periphery of said impeller;

means defining an unobstructed transfer duct communicating with said pumping chamber outlet, said duct means having spaced upper and loWer surfaces, said lower surface extending into said diffusing layer and communicating with a generally tangentially directed fluid outlet from said transfer duct in said diffusing chamber; and,

each diffusing chamber having a series of inwardly spiralling vanes disposed to provide first passage of expanding cross-sectional area between one of said vanes and the outer casing of said chambers and then forming passages of uniform cross-sectional area between said vanes, said vanes terminating in an outlet from said diffusion chamber which forms a cooperative intake for the next stage.

3. The apparatus of claim 2 wherein said intake to said pumping chamber and said outlet from said diffusing chamber are offset from the axis of said cylinder but aligned with respect to each other and the axis of said impellers in said pumping chambers.

4. A multi-stage pump comprising:

an outer casing in the form of a right cylinder;

a series of substantially flat, axially spaced, generally parallel Walls transverse the axis of said cylinder dividing said cylinder into a series of alternate upstream pumping chambers and downstream diffusing chambers;

each pumping chamber including a fluid impeller cooperatively mounted for rotation in said pumping chamber, a central fluid inlet disposed to conduct fluid to said impeller and a vane spiralling radially outward about a portion of the periphery of the said impeller and forming a volute between said vane and said outer casing, said vane terminating in a tangentially directed pumping chamber outlet adjacent the periphery of the said impeller;

means defining an unobstructed transfer duct communicating with said pumping chamber outlet and forming a substantial continuation of said volute around the periphery of said stage but progressing gradually in an axial direction to a generally tangentially directed fluid outlet from said transfer duct in said diffusing chamber; and,

each diffusing chamber having a series of inwardly spiralling vanes providing first passage of expanding cross-sectional area between one of said vanes and the outer casing of said chamber and then forming passages of uniform cross-sectional area between adjacent said vanes, said vanes terminating in a central outlet from said diffusing chamber which forms a central intake for the next stage.

5. The multi-stage compressor of claim 4 in which said diffusing segments extend around said diffusing chambers for at least from said transfer duct.

6. The multi-stage compressor of claim 4 in which said central outlet from said diffusing chamber includes a flanged rim of one diameter directed in a downstream direction; and, said impeller includes a central inlet hav ing a flanged rim directed in an upstream direction and of greater diameter than said compressor outlet rim, said diffusing chamber outlet and said impeller inlet being disposed in nesting cooperative relation to provide flow passage from said diffusing chamber to said impeller.

(References on following page) 7 References Cited by the Examiner UNITED STATES PATENTS 131,076 11/1917 Allen 230 130 906894 1/1925 Spillman 103 10s 5 228,365 12/1951 Watson 230130 103,721

4/1961 Lung 103-108 12/1965 Bochl 230-130 3/1966 McMahon 230130 FOREIGN PATENTS 3/ 1901 Germany.

8/ 1956 Germany.

2/ 1925 Great Britain. 3/ 1924 Switzerland.

MARK NEWMAN, Primary Examiner.

HENRY F. RADUAZO, Examiner. 

1. A MULTI-STAGE PUMPING DEVICE COMPRISING: A RIGHT CYLINDRICAL OUTER CASING; AT LEAST ONE FLUID CONDUCTING STAGE IN SAID CASING, EACH STAGE INCLUDING MEANS DEFINING AN UPSTREAM PUMPING CHAMBER AND A DOWNSTREAM DIFFUSING CHAMBER; EACH PUMPING CHAMBER INCLUDING A FLUID IMPELLER COOPERATIVELY MOUNTED FOR ROTATION IN SAID PUMPING CHAMBER, A CENTRAL FLUID INLET DISPOSED TO CONDUCT FLUID TO SAID IMPELLER AND A VANE SPIRALLING RADIALLY OUTWARD ABOUT A PORTION OF THE PERIPHERY OF SAID IMPELLER AND FORMING A VOLUTE BETWEEN SAID VANE AND SAID OUTER CASING, SAID VANE TERMINATING IN A GENERALLY TANGENTIALLY DIRECTED PUMPING CHAMBER OUTLET ADJACENT THE PERIPHERY OF SAID IMPELLER; MEANS DEFINING AN UNOBSTRUCTED TRANSFER DUCT COMMU- 